We have an amazing rescue story. It was all caught on tape. It happened on a tiny island, where a team of snorkelers were saved after a helicopter spotted their S.O.S. Message, there drawn in the sand. Ryan smith has this story for us. Reporter: We were very lucky we didn't have a different outcome. That's what real-life castaways told us about being stranded on a desert island. Watch as this Australian rescue plane, searching for five missing people stumbles on a giant clue. A massive S.O.S., scrawled in the sand of a tiny island. An almost cinematic moment, like from the movie "Castaway." Their day began what was supposed to be a fun day of snorkeling. It was a great day to be boating. Reporter: After dropping anchor to explore, their boat drifted away, leaving them marooned without food and water or cell phones. Went off down the sand bar. Reporter: The group grew desperate, hoping their S.O.S. Wouldn't be washed away by the tide. And fearing they could be in store for a long wait. Or worse. We did suspect that we would be hunkered down on the rocks for the night. So, that wasn't -- that was a fairly grim prospect. We didn't -- Reporter: In an incredible stroke of luck, another boat spotted the drifting vessel out at sea and alerted authorities. We wrote in the sand. We knew this must be them. Reporter: And find them, they did, after nine harrowing hours on the island. Rescuers seen here lowering down to the rocky surface of the island. And whisking them to safety. We very very, very lucky. It would have been a different outcome. Reporter: All thanks to a lot of luck and that message written in the stand. And Lynn, the woman you saw there, told us she knows they were at great risk. But even so, she can't wait to get back out there and spend another day in what she calls, paradise.

This transcript has been automatically generated and may not be 100% accurate.

{"id":23451265,"title":"Snorkeling Party Rescued Off Australia's Coast","duration":"2:09","description":"Five real-life castaways were rescued after nine hours on an island thanks to a message in the sand.","url":"/GMA/video/snorkeling-rescue-castaways-rescued-off-australias-coast-23451265","section":"GMA","mediaType":"default"}